Add a run-make test for Arm target-cpu features.

tests/run-make/arm-target-cpu-features/cortex-m7.checks

@@ -0,0 +1,7 @@
+// Cortex-M7 does not have Advanced SIMD, so don't check anything in vadd_f32_q.
+CHECK-LABEL: vadd_f32_q:
+
+// Cortex-M7 enables double-precision.
+CHECK-LABEL: vadd_f64:
+CHECK: vadd.f64 d0, d0, d1
+CHECK: bx lr

tests/run-make/arm-target-cpu-features/cortex-m85.checks

@@ -0,0 +1,12 @@
+// Cortex-M85 enables the Helium instructions.
+CHECK-LABEL: vadd_f32_q:
+CHECK: vld{{.*}}
+CHECK: vld{{.*}}
+CHECK: vadd.f32{{.*}}q
+CHECK: vst{{.*}} [r0]
+CHECK: bx lr
+
+// Cortex-M85 enables double-precision.
+CHECK-LABEL: vadd_f64:
+CHECK: vadd.f64 d0, d0, d1
+CHECK: bx lr

tests/run-make/arm-target-cpu-features/lib.rs

@@ -0,0 +1,13 @@
+#![no_std]
+
+#[no_mangle]
+pub fn vadd_f32_q(x: &mut [f32; 4], y: &[f32; 4]) {
+    for i in 0..4 {
+        x[i] += y[i];
+    }
+}
+
+#[no_mangle]
+pub fn vadd_f64(x: f64, y: f64) -> f64 {
+    x + y
+}

tests/run-make/arm-target-cpu-features/rmake.rs

@@ -0,0 +1,55 @@
+// This tests that target-cpu correctly enables additional features for some Arm targets.
+// These targets were originally defined in such a way that features provided by target-cpu would be
+// disabled by the target spec itself. This was fixed in #123159.
+
+// FIXME: This test should move to tests/assembly when building without #![no_core] in
+// that environment is possible, tracked by #130375.
+
+use run_make_support::{llvm_filecheck, llvm_objdump, rustc, static_lib_name};
+
+struct TestCase {
+    target: &'static str,
+    cpu: &'static str,
+}
+
+static CASES: &[TestCase] = &[
+    TestCase { target: "thumbv7em-none-eabihf", cpu: "cortex-m7" },
+    TestCase { target: "thumbv8m.main-none-eabihf", cpu: "cortex-m85" },
+];
+
+fn main() {
+    for case in CASES {
+        let lib = static_lib_name(case.cpu);
+        let checks = format!("{}.checks", case.cpu);
+
+        let rustc_command = || {
+            let mut cmd = rustc();
+            cmd.edition("2021")
+                .target(case.target)
+                .arg("-Copt-level=3")
+                .crate_type("rlib")
+                .input("lib.rs")
+                .output(&lib);
+            cmd
+        };
+
+        let objdump_command = || {
+            let mut cmd = llvm_objdump();
+            cmd.arg("--arch-name=arm")
+                .arg(format!("--mcpu={}", case.cpu))
+                .disassemble()
+                .input(&lib);
+            cmd
+        };
+
+        // First, run without target-cpu and confirm that it fails.
+        rustc_command().run();
+        let dis = objdump_command().run().stdout_utf8();
+        llvm_filecheck().patterns(&checks).stdin_buf(dis).run_fail();
+
+        // Then, run with target-cpu and confirm that it succeeds.
+        rustc_command().arg(format!("-Ctarget-cpu={}", case.cpu)).run();
+        let dis = objdump_command().run().stdout_utf8();
+        llvm_filecheck().patterns(&checks).stdin_buf(dis).run();
+    }
+}